Problem: Before the previous stop there were 35 people riding on a train. 28 people ended up getting off at the stop. How many people are riding the train now?
Explanation: The number riding the train now is the difference between the number who were riding and the number who got off at the previous stop. The difference is $35 - 28$ people on the train. $35 - 28 = 7$ people are on the train.